In conventional distributor type ignition systems which utilise a single ignition coil, and engine analyser may be provided with a signal comprising a series of pules each identifying the start of each cylinder ignition sequence, by connecting the analyser to the low tension side of the coil, between the coil and contact breaker. With multi-coil ignition systems a separate coil is provided for each spark plug or pair of spark plugs. Each coil is connected between a power supply and switching means by which it may be selectively connected to earth. There is consequently no common point in the ignition system at which a signal identifying the start of each cylinder ignition sequence can be obtained.